TaskID represents the immutable and unique identifier for
a Map or Reduce Task. Each TaskID encompasses multiple attempts made to
execute the Map or Reduce Task, each of which are uniquely indentified by
their TaskAttemptID.
TaskID consists of 3 parts. First part is the JobID, that this
TaskInProgress belongs to. Second part of the TaskID is either 'm' or 'r'
representing whether the task is a map task or a reduce task.
And the third part is the task number.
An example TaskID is :
task_200707121733_0003_m_000005 , which represents the
fifth map task in the third job running at the jobtracker
started at 200707121733.

Applications should never construct or parse TaskID strings
, but rather use appropriate constructors or forName(String)
method.